This invention relates to horn type radiators for measurement of the near-field radiation patterns of electromagmetic radiation apparatus and, more particularly, to a horn having a polarizer and an orthomode tee for conversion between circularly polarized radiation of both senses and corresponding linearly polarized waves, the tee including a multiple blade type structure for isolating the linearly polarized waves.
The testing of radiation apparatus, such as various forms of radiators and array antennas, is important to insure that such an apparatus produces a desired radiation pattern and/or responds in a desired fashion to incident radiation. One form of testing of the radiation apparatus involves the measurement of the near-field radiation response in an anechoic chamber. Such testing may include the use of circularly polarized radiation with both right and left-handed polarizations being employed. Also, it is desirable to employ a radiator of the test equipment which is sufficiently unobtrusive, in a radiation sense, so as to avoid introduction of any perturbations to the radiation pattern being measured. It is also desirable that the radiation characteristics of the radiator employed for performing the test should have a uniform radiation pattern as measured in directions off of a central axis of symmetry of the radiation pattern.
A problem arises in that previously available probes for RF (radio frequency) radiation which are to be used for near-field radiation measurements have not met all of the foregoing requirements to the extent which would be desirable. Typically, such probes have employed a coaxial dipole or an open-ended waveguide for linear polarization, and a cross-dipole or a helix for circular polarization. In particular, it is noted that the electrical performances of the previously available probes are not able to meet the requirements of current state-of-the-art near-field computerized antenna range pattern measurements.